The present invention relates to a composite containing thin film particles having a carbon skeleton, a method for reducing the thin film particles and a process for the production of the composite. More specifically, it relates to a composite containing thin film particles having a carbon skeleton which composite is suitable for various uses such as a high strength material, a material having a small heat-deformation, a material having high barrierability to small molecules or the like, a material having a high thermal conductivity and an electrically-conductive material used for a circuit or the like, a method for reducing the above thin film particles and a process for the production of the above composite.
In recent years, searches for materials having high anisotropy of shape and applications thereof are proceeding rapidly. As an anisotropic shape material having carbon atoms as a skeleton, there are known one-dimensional materials such as a graphite fiber or a carbon nanotube being an especially slender graphite fiber and two-dimensional materials such as graphite, graphite fluoride and graphite oxide. Of these, each of graphite, graphite fluoride and graphite oxide is a multi-layer structure matter in which two-dimensional fundamental layers are laminated, and multi-layer structure matters having so many layers are generally known. Concerning graphite oxide, very thin graphite oxide having a small number of layers has been made (for example, N. A. Kotov et al., Adv.Mater., 8,637(1996)). The present inventors also have found a process for producing thin film particles of such graphite oxide (when the number of layers is one, e.g., it is preferred to call it xe2x80x9cgraphene oxidexe2x80x9d (xe2x80x9cgraphenexe2x80x9d is the name for one graphite layer)) in high yield and produced thin film particles having a very small number of layers similar to graphite (when the number of layers is one, it is preferred to call it xe2x80x9cgraphenexe2x80x9d) by reducing the above thin film particles (JP-A-2002-53313). Further, the present inventors have produced especially broad thin film particles, a lamination layer aggregate in which the thin film particles are laminated and broad, and reductants of these (Japanese Patent Application No. 2001-374537, Japanese Patent Application No. 2001-374538).
The fundamental layer of graphite oxide is thought to have a structure in which acidic hydroxyl groups, etc., are bonded to both sides of a carbon skeleton (composed of sp3 carbon and sp2 carbon, sp3 carbon is larger in amount) having a thickness equivalent to one carbon atom or two carbon atoms (for example, T. Nakajima et al., Carbon, 26, 357(1988); M. Mermoux et al., Carbon, 29, 469(1991)). When the thickness of the carbon skeleton is equivalent to the size of one carbon atom, and hydroxyl groups are bonded to both sides of the carbon skeleton and interlayer water is remarkably little in amount, the thickness of the fundamental layer is 0.61 nm. Further, when graphite oxide has a high oxidation degree and is dried sufficiently, the content of oxygen in the graphite oxide is approximately 30 to 40 wt %.
Although the above graphite oxide having an oxygen content of approximately 30 to 40 wt % generally has a high resistivity of about 106 to 108 xcexa9xc2x7cm and has remarkably low electric conductivity, it is known that the above graphite oxide comes to have an electronic state having many sp2 bonds analogous to graphite by partial or complete reduction and is thus increased in electric conductivity. The graphite oxide increased in electric conductivity by the reduction can be applied, as a semiconductor or a conductor, in various fields such as semiconductor devices, wiring materials, fillers for anti-electrification and anti-electrostatic, so that it is remarkably useful.
The present inventors have disclosed thin film particles which are obtained by oxidizing graphite and which have a thickness of 0.4 to 10 nm and a planar direction size of 20 nm or more, are dispersible in a liquid having a relative dielectric constant of 15 or more and have a carbon skeleton in JP-A-2002-53313. In the specification thereof, the present inventors indicate that heating, a reducing agent or an electrode reaction can reduce the thin film particles. Further, the present inventors have disclosed large-sized thin film particles having a carbon skeleton of a planar-direction size of 500 xcexcm or more in Japanese Patent Application No. 2001-374537 and similarly indicated that heating, a reducing agent or an electrode reaction can reduce these thin film particles too.
The above thin film particles of graphite oxide (to be referred to as xe2x80x9coxidized form thin film particlesxe2x80x9d hereinafter) are increased in electric conductivity by partial or complete reduction, as described above. In particular, as a general behavior of graphite oxide, reduction by heating can convert even the inside of a multi-layer particle into a structure similar to that of graphite. It is known that, when heating is carried out in a state where a plurality of the particles are bonded to each other, intermolecular forces arise in an interlayer inside each multi-layer particle or between a plurality of the particles so that a macroscopic shape like a general graphite film can be provided (J. Maire et al., Carbon, 6,555(1968)). The oxidized form thin film particles are converted into reduced form thin film particles by similar heating (JP-A-2002-53313).
Here, when the thin film particles are completely reduced, each fundamental layer of the thin film particles becomes almost graphite""s fundamental layer (graphene). When the thin film particles are multi-layer particles, the interlayer distance is almost equal to the interlayer distance of graphite. However, each multi-layer particle has a structure of a turbostratic tendency in which the mutual positional relationship of respective layers is more turbulent than that of graphite. Further, when the thin film particles are partially reduced, oxygen and the like remain in each fundamental layer and its interlayer distance becomes larger than that of graphite.
The above oxidized form and reduced form thin film particles can be called xe2x80x9cgraphite oxide nanofilmxe2x80x9d (xe2x80x9cgraphene oxide nanofilmxe2x80x9d, when the number of layers is one), when the fraction of oxygen is high. When the oxygen fraction is low or no oxygen is contained, the thin film particles can be called xe2x80x9cgraphite nanofilmxe2x80x9d (xe2x80x9cgraphene nanofilmxe2x80x9d, when the number of layers is one). Further, uniformly, these thin film particles are respectively called an oxidized form single-layer carbon nanofilm or multilayer carbon nanofilm and a reduced form single-layer carbon nanofilm or multilayer carbon nanofilm. Using the name of xe2x80x9ccarbon nanofilmxe2x80x9d can prevent any confusion from being caused by calling the thin film particles having a turbostratic tendency xe2x80x9cgraphitexe2x80x9d, as described above.
Concerning such oxidized form and reduced form thin film particles, there have been synthesized some composites with a macromolecule. These composites are intercalation compounds of the thin film particles and the macromolecule. Although their interlayer distances (interval of a fundamental period of a layer structure) depend upon a mixing ratio or additives at the time of synthesis, it is reported that the interlayer distance of a composite with poly(ethylene oxide) is 1.28 nm (Y. Matsuo et al., Carbon, 34, 672(1996), polyethylene oxide is added), that the interlayer distance of a composite with polyaniline is 1.2 nm (S. Higashika et al., Carbon, 37, 351(1999), aniline (monomer) is polymerized in interlayer spaces), and that the interlayer distance of a composite with poly(vinyl acetate) is 1.15 nm (P. Liu et al., Carbon, 37, 2073(1999), vinyl acetate (monomer) is polymerized in interlayer spaces).
However, each of these synthesis examples contains a relatively high fraction of the thin film particles. These examples target a composite having high periodicity, the whole of which is an intercalation compound. In contrast, there have not been reported a composite with a macromolecule in which the majority of thin film particles contained is relatively randomly located, like a general composite material obtained by simply mixing a reinforcing component such as a filler and a matrix component, and a composite formed by covalent-bonding a lot of thin film particles to each other with low molecular-weight parts.
From a wider standpoint, further, there is known a composite containing planar particles obtained by peeling particularly a lamellar clay mineral (silicate) (for example, K. Yano et al., J.Appl.Polym.Sci., 49, 1259(1993)) as a composite of two-dimensional particles having an anisotropic shape, like the above thin film particles, with a macromolecule. Further, a composite containing a carbon nanotube (for example, X. Gong et al., Chem.Mater., 12, 1049(2000)) is known as a composite of carbonaceous particles having an anisotropic shape with a macromolecule. Each of these composites is a random composite.
Even when such a random composite contains a relatively small amount of the thin film particles, the composite easily obtains various properties such as high strength. Further, it is thought that, since the anisotropy of the composite as a whole is low, the composite is easy to handle. Further, the production of the composite becomes relatively easy if it is possible by a simple mixing.
It is an object of the present invention to provide a composite having a relatively low periodicity which composite is formed of thin film particles and a macromolecule or the thin film particles and a reactive compound, a method for reducing the thin film particles and a process for the production of the above composite.
According to the present invention, there is provided a composite formed of a component (a) or a component (b) and a component (c), or the component (a) or the component (b) and a component (d),
(a) oxidized form thin film particles which are obtained by oxidizing graphite, have a carbon skeleton, have a thickness of 0.4 nm to 10 nm and a planar-direction size of at least 20 nm and have lyophilic to a liquid having a relative dielectric constant of at least 15,
(b) reduced form thin film particles obtained by partially or completely reducing the above thin film particles so as to have an oxygen content of 0 to 35 wt %,
(c) a macromolecule as a matrix component, and
(d) low molecular-weight parts which bond a plurality of the thin film particles by a covalent bond.
According to the present invention, further, there is provided a composite according to the above, wherein the reduced form thin film particles are obtained by heating a dispersion in a liquid of thin film particles which have a carbon skeleton, have a thickness of 0.4 nm to 100 nm and a planar-direction size of at least 20 nm, are obtained by oxidizing graphite, and are dispersible in a liquid having a relative dielectric constant of at least 15, at 130xc2x0 C. or higher, to reduce the thin film particles while holding the dispersed state of the thin film particles.
According to the present invention, further, there is provided a composite according to the above, wherein the reduced form thin film particles are obtained by irradiating thin film particles which have a thickness of 0.4 nm to 100 nm and a planar-direction size of at least 20 nm, are obtained by oxidizing graphite, have a carbon skeleton and are dispersible in a liquid having a relative dielectric constant of at least 15, with light.
According to the present invention, further, there is provided a process for the production of the above composite formed of thin film particles and a macromolecule, which process comprises mixing a dispersion of oxidized form thin film particles with a macromolecule which is in a molten state or in the state of a solution, then removing a dispersion medium of the dispersion or the dispersion medium and a solvent of the solution.
According to the present invention, further, there is provided a process for the production of the above composite formed of thin film particles and a macromolecule, which process comprises mixing a dispersion of oxidized form thin film particles with a polymerizable compound or a solution of the polymerizable compound, polymerizing the polymerizable compound to convert it into a macromolecule and removing a dispersion medium of the dispersion or the dispersion medium and a solvent of the solution.
According to the present invention, further, there is provided a process for the production of the above composite formed of thin film particles and low molecular-weight parts which bond the thin film particles to each other, which process comprises mixing a dispersion of oxidized form thin film particles with a reactive compound having at least one functional group which can form a covalent bond with the thin film particles or a solution of the above reactive compound to bond a plurality of the thin film particles to each other by covalent bonds and removing a dispersion medium of the dispersion or the dispersion medium and a solvent of the solution.
According to the present invention, further, there are provided uses of the above composite as a variety of materials.
According to the present invention, further, there is provided a method for reducing thin film particles which are obtained by oxidizing graphite, have a carbon skeleton and are dispersible in a liquid having a relative dielectric constant of at least 15, which method comprises heating a dispersion of the thin film particles in a liquid at 130xc2x0 C. or higher, to reduce the thin film particles while holding the dispersed state of the thin film particles.